Method for joining members

ABSTRACT

In the present invention, a method for joining members involves preparing a steel component having a bottom wall in which a hole is provided, and a hollow aluminum pipe. The aluminum pipe is slipped through the hole in the steel component and passed through the bottom wall, rubber is inserted into the interior of the aluminum pipe, and the rubber is compressed in the direction of the axis (L) of the aluminum pipe and induced to distend towards the outside from the inside. As a result of the foregoing, at least a section of the aluminum pipe slipped through the hole is induced to undergo expansion and is joined by clinching to the bottom wall. This method for joining members reduces the load on the members, improves the joint strength, and enables two members to be joined at reduced cost.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.15/546,021 filed Jul. 25, 2017, which is the U.S. National Phase ofInternational Application No. PCT/JP2016/050046 filed Jan. 4, 2016,which claims priority from Japanese Patent Application Nos. 2015-124075filed Jun. 19, 2015 and 2015-022573 filed Feb. 6, 2015.

TECHNICAL FIELD

The present invention relates to methods for joining members.

BACKGROUND ART

In order to achieve weight reduction and improved safety in automobiles,high-strength steel sheets composed of so-called high-tensile steel areused. Although effective for weight reduction and improved safety, suchhigh-tensile steel is still heavy compared with low specific gravitymaterials, such as aluminum. Moreover, high-tensile steel is problematicin terms of low formability due to its high strength, increasing formingload, and also low dimensional accuracy. In order to solve theseproblems, a multi-material process that involves using a steel componenttogether with an extruded product, a molded product, or a press-formedproduct that use aluminum, which has lower specific gravity than steelsheets, has been performed in recent years.

A problem with this multi-material process is in the joining of thesteel component and the aluminum component. In the welding technologytypified by spot-welding, fragile intermetallic compounds (IMC) occur atthe interface between the steel sheet and the aluminum sheet. Thus,joining techniques, such as an electromagnetic-forming joiningtechnique, a screw-fastening technique typified by bolts and nuts, afriction-stir-welding (FSW) technique, a riveting technique, aself-piercing-riveting (SPR) technique, a mechanical clinchingtechnique, and a bonding technique, are put to practical use.

A clinching process based on electromagnetic forming involves insertinga solenoid forming coil into a pipe-shaped component fitted to acounterpart component and causing induced current to occur in the pipeserving as a conductor in accordance with a changing magnetic fieldoccurring as a result of applying impulse current to the coil. Anelectromagnetic force is generated between the magnetic field caused byprimary current in the coil and the induced current flowing oppositelyin the circumferential direction of the pipe, and the pipe receives anoutward force and thus expands, thereby becoming clinched to thecounterpart component. This joining method is suitable for copper andaluminum, which have high electric conductivity, and is put to practicaluse in some techniques for joining together automobile components.

Patent Literature 1 discloses a clinching technique based onelectromagnetic forming for performing a multi-material process. InPatent Literature 1, a bumper reinforcement member formed of a metallicmaterial that is hollow in cross section is caused to expand byelectromagnetic forming and is engaged with holes provided in a bumperstay composed of an aluminum alloy so as to be joined thereto.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2007-284039

SUMMARY OF INVENTION Technical Problem

As in Patent Literature 1, electromagnetic forming is suitable forclinching a hollow component composed of copper or aluminum having highelectric conductivity to a counterpart component, and a circular shapeis preferred due to this joining mechanism.

However, the joining technique based on electromagnetic forming requiresthat the inner diameter of the solenoid coil to be used be smaller thanthat of the aluminum component (i.e., aluminum pipe). When the diameterof a coil is to be reduced when joining together small-diametercomponents, there are problems in terms of difficulties in manufacturingof the coil, as well as performance and durability thereof. With regardto difficulties in manufacturing, it is difficult to form a conductorinto the shape of a coil, leading to stricter limitations with respectto the material and the cross-sectional shape of the conductor. Inaddition, the conductor cross-sectionally deforms when being formed intothe shape of a coil. Moreover, a new capital investment becomesnecessary, such as requiring a large-capacity high-voltage capacitor.Furthermore, the joining is not possible if the aluminum component hasan angular cross-sectional shape, a hole, or a slit.

An object of the present invention is to provide a method for joiningmembers, by which two members can be joined together at low cost whilereducing the load on the members and increasing the joint strength.

Solution to Problem

The present invention provides a joining method including: preparing afirst member and a hollow second member, the first member having a firstsection provided with a first hole; fitting the second member into thefirst hole in the first member so as to cause the second member toextend through the first section; inserting an elastic body into thesecond member; and compressing the elastic body in a direction of anaxis of the second member so as to cause the elastic body to expand froman inner side toward an outer side, and thus causing at least a part ofthe second member fitted in the first hole to expand so as to becomeclinched to the first section.

According to this method, the elastic body is caused to expand outwardso that the second member expands uniformly, thereby preventing localdeformation and reducing the load on the members. This is because thesecond member can be uniformly deformed by utilizing the properties inwhich the elastic body compressed in the direction of the axis expandsuniformly from the inner side toward the outer side. Therefore, fitaccuracy can be improved, thereby achieving increased joint strength.Moreover, this is an easier method, as compared with an electromagneticforming method or other machining methods. An electromagnetic formingmethod is usable only on electrically conductive materials and haslimitations with respect to cross-sectional shapes and dimensionsdepending on coils to be used. In contrast, this method is not dependenton materials and has no limitations related to cross-sectional shapesand dimensions. Moreover, since the method is executable in a facilitythat applies a compressive force to the elastic body, an electricalfacility that requires a large-capacity capacitor is not necessary.Consequently, the two members can be joined together at low cost.

Furthermore, a shape of the first hole in the first member may beanalogous to a cross-sectional shape of the part of the second memberfitted in the first hole.

According to this method, the first member and the second member haveshapes analogous to each other so that the joining process can beperformed by causing the second member to expand uniformly, therebypreventing local load from occurring in the first member and the secondmember.

Furthermore, an outer-frame mold may be disposed at the outer side ofthe second member, and at least a part of the second member may beformed to extend along the outer-frame mold so as to become clinched.

According to this method, the second member can be deformed to afreely-chosen shape by using outer-frame molds with variousinner-surface shapes. The deformation shape can be appropriatelyselected in view of, for example, component performance and can be setin accordance with the intended purpose.

Furthermore, an outer-frame mold may be disposed at the outer side ofthe second member, and clinching may be performed while partiallylimiting expansion of the second member by using the outer-frame mold.

According to this method, by disposing the outer-frame mold, anexpanding region of the second member is regulated, so that theexpanding region can be controlled with high accuracy. This expandingregion refers to a region in which the second member expands outward.

Furthermore, the second member may also be compressed in the directionof the axis when the elastic body is compressed.

According to this method, the second member is also compressed in thedirection of the axis so as to assist with outward expansion of thesecond member. Specifically, together with the expanding force appliedby the elastic body from the inner side of the second member, the secondmember can be expanded more reliably, thereby enabling clinching.

Furthermore, an edge of the first hole may be burred.

According to this method, the edge of the hole in the first member isburred so that the strength of the hole and the first section of thefirst member can be increased. Consequently, the first member can beprevented from deforming, the second member can be prevented from beingdamaged, and the joint strength between the two members can beincreased.

Furthermore, a surface different from a surface provided with the firsthole may have a bead section protruding in the direction of the axis,and clinching may be performed by including the bead section.

According to this method, because clinching is performed by includingthe bead section, the two members can be fixed to each other moresecurely, and the joint strength therebetween can be further increased.In particular, in a case where the second member has a circularcross-sectional shape, the second member can be prevented from rotatingrelative to the first member.

Furthermore, the first member may include a second section having asecond hole and may be clinched to the second member at the first holeand the second hole.

According to this method, clinching is performed at two locations sothat the joint strength can be further increased, as compared with thecase where clinching is performed at a single location.

Furthermore, the elastic body may be split at a joining section betweenthe first member and the second member.

According to this method, the elastic body is split at the joiningsection so that deformation of the joining section of the first membercan be prevented. Specifically, the elastic body is split such that theelastic body is not disposed near the joining section, whereby thesecond member does not receive an expanding force from the elastic bodynear the joining section and thus does not expand near the joiningsection. Consequently, the first member does not receive a force fromthe second member near the joining section, so that the shape of thejoining section can be maintained.

Furthermore, a plate may be inserted between split pieces of the elasticbody.

According to this method, the plate exists in the joining section sothat deformation of the joining section of the first member can beprevented more reliably. Because the plate does not expand even byreceiving a compressive force in the direction of the axis, an expandingforce is not applied to the joining section, so that the joining sectioncan maintain its original shape more reliably.

Furthermore, the second member may include an outer wall provided with apartition wall therein and extending in the direction of the axis, andclinching may be performed by inserting a plurality of the elasticbodies in spaces partitioned by the partition wall.

According to this method, because the clinching process is performed byusing the plurality of elastic bodies, concentration of stress caused bydeformation can be prevented, so that the load on the first member andthe second member can be reduced.

Furthermore, the second member may include an end surface inclinedrelative to the axis, and opposite end surfaces of the elastic body inthe direction of the axis may be parallel to the inclined surface.

Accordingly, this method can be used for clinching the first member andthe second member together in an inclined state, which is often seenfrom a practical standpoint. In particular, opposite end surfaces of theelastic body are given the same angle as the joining angle, so that theelastic body expands uniformly, whereby the second member can beexpanded uniformly.

Furthermore, the first member may include an upright wall parallel tothe axis, and clinching may be performed while restraining deformationof the upright wall by using a fixation jig.

According to this method, deformation of the first member is restrainedby the jig, so that deformation of the first member caused by expansionof the second member can be suppressed.

Advantageous Effects of Invention

According to the present invention, the second member is caused toexpand uniformly by causing the elastic body to expand from the innerside toward the outer side, thereby preventing local deformation andreducing the load on the members. Therefore, fit accuracy can beimproved, thereby achieving increased joint strength. Moreover, sincethis is an easier method, as compared with an electromagnetic formingmethod or other machining methods, the two members can be joinedtogether at low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a perspective view of a channel-type steel component having acircular hole and an aluminum pipe having a circular cross-sectionalshape.

FIG. 1B is a perspective view of the steel component and the aluminumpipe in FIG. 1A in a clinched state.

FIG. 2A is a cross-sectional view illustrating a state before aclinching process according to a first embodiment of the presentinvention.

FIG. 2B is a cross-sectional view illustrating a state where theclinching process according to the first embodiment of the presentinvention is being performed.

FIG. 2C is a cross-sectional view illustrating a state after theclinching process according to the first embodiment of the presentinvention.

FIG. 2D is a cross-sectional view illustrating a state where a rubberpiece is being pulled out after the clinching process according to thefirst embodiment of the present invention.

FIG. 3A is a cross-sectional view illustrating a state before theclinching process when a rubber piece according to a modification of thefirst embodiment of the present invention is a fluid sealing member.

FIG. 3B is a cross-sectional view illustrating a state after theclinching process when the rubber piece according to the modification ofthe first embodiment of the present invention is a fluid sealing member.

FIG. 4A is a perspective view of a steel component having a circularhole and an aluminum pipe having a rectangular cross-sectional shape.

FIG. 4B is a perspective view of a steel component having a rectangularhole and an aluminum pipe having a circular cross-sectional shape.

FIG. 5A is a cross-sectional view of an example of a joining section ofa steel component having undergone a burring process.

FIG. 5B is a cross-sectional view of another example of a joiningsection of a steel component having undergone a burring process.

FIG. 5C is a cross-sectional view of another example of a joiningsection of a steel component having undergone a burring process.

FIG. 6A is a perspective view of a joining section of a steel componenthaving a circular hole having undergone a burring process.

FIG. 6B is a perspective view of a joining section of a steel componenthaving a rectangular hole having undergone a burring process.

FIG. 7A is a cross-sectional view illustrating a state before aclinching process performed by using an outer-frame mold according to asecond embodiment of the present invention.

FIG. 7B is a cross-sectional view illustrating a state after theclinching process performed by using the outer-frame mold according tothe second embodiment of the present invention.

FIG. 8A is a perspective view of an aluminum pipe formed into acylindrical tube shape.

FIG. 8B is a perspective view of an aluminum pipe formed into ahexagonal tube shape.

FIG. 8C is a perspective view of an aluminum pipe formed into a crosstube shape.

FIG. 9A is a cross-sectional view illustrating a state before aclinching process performed by disposing a rubber piece only near ajoining section in accordance with a third embodiment of the presentinvention.

FIG. 9B is a cross-sectional view illustrating a state after theclinching process performed by disposing the rubber piece only near thejoining section in accordance with the third embodiment of the presentinvention.

FIG. 10A is a cross-sectional view illustrating a state before aclinching process in which an aluminum pipe is partially expanded byusing an outer-frame mold according to a modification of the thirdembodiment of the present invention.

FIG. 10B is a cross-sectional view illustrating a state after theclinching process in which the aluminum pipe is partially expanded byusing the outer-frame mold according to the modification of the thirdembodiment of the present invention.

FIG. 11A is a cross-sectional view illustrating a state before aclinching process performed by using a truncated-cone-shaped indenteraccording to a fourth embodiment of the present invention.

FIG. 11B is a cross-sectional view illustrating a state after theclinching process performed by using the truncated-cone-shaped indenteraccording to the fourth embodiment of the present invention.

FIG. 12A is a cross-sectional view illustrating a state before aclinching process performed by compressing an aluminum pipe according toa fifth embodiment of the present invention in an axial direction.

FIG. 12B is a cross-sectional view illustrating a state after theclinching process performed by compressing the aluminum pipe accordingto the fifth embodiment of the present invention in the axial direction.

FIG. 13A is a cross-sectional view illustrating a state before aclinching process performed by using an indenter equipped with an outerframe in accordance with a modification of the fifth embodiment of thepresent invention.

FIG. 13B is a cross-sectional view illustrating a state after theclinching process performed by using the indenter equipped with theouter frame in accordance with the modification of the fifth embodimentof the present invention.

FIG. 14A is a perspective view of a steel component having a circularhole and an aluminum pipe having a circular cross-sectional shape whenthe two are clinched together at two locations in accordance with asixth embodiment of the present invention.

FIG. 14B is a perspective view of a steel component having a rectangularhole and an aluminum pipe having a rectangular cross-sectional shapewhen the two are clinched together at two locations in accordance withthe sixth embodiment of the present invention.

FIG. 15A is a perspective view of a hat-channel-type steel componenthaving a circular hole and an aluminum pipe having a circularcross-sectional shape when the two are clinched together at twolocations in accordance with a modification of the sixth embodiment ofthe present invention.

FIG. 15B is a perspective view of a hat-channel-type steel componenthaving a rectangular hole and an aluminum pipe having a rectangularcross-sectional shape when the two are clinched together at twolocations in accordance with a modification of the sixth embodiment ofthe present invention.

FIG. 16 is a cross-sectional view illustrating a state where theclinching process in FIGS. 15A and 15B is being performed.

FIG. 17A is a cross-sectional view illustrating a state after theclinching process in FIG. 16A.

FIG. 17B is a cross-sectional view illustrating a state after theclinching process in FIG. 16A is performed by partial expansion.

FIG. 18A is a cross-sectional view illustrating a state after a steelcomponent and an aluminum pipe are clinched together at surfaces havingbead sections in accordance with a modification of a seventh embodimentof the present invention.

FIG. 18B is a cross-sectional view taken along line XVIII-XVIII in FIG.18A.

FIG. 19 is a cross-sectional view illustrating a state after a clinchingprocess performed by using split rubber pieces according to an eighthembodiment of the present invention.

FIG. 20A is a cross-sectional view illustrating a state after aclinching process performed by inserting a plate between split rubberpieces in accordance with a modification of the eighth embodiment of thepresent invention.

FIG. 20B is a cross-sectional view illustrating a state after aclinching process performed by using a rubber piece with a differenthardness at a joining section in accordance with a modification of theeighth embodiment of the present invention.

FIG. 21A is a perspective view illustrating a state before a resinoustube component and an aluminum pipe according to a ninth embodiment ofthe present invention are clinched together.

FIG. 21B is a perspective view illustrating a state after the resinoustube component and the aluminum pipe in FIG. 21A are clinched together.

FIG. 22A is a cross-sectional view illustrating the state before theresinous tube component and the aluminum pipe in FIG. 21A are clinchedtogether.

FIG. 22B is a cross-sectional view illustrating the state after theresinous tube component and the aluminum pipe in FIG. 21A are clinchedtogether.

FIG. 23 is a perspective view of a steel bumper beam and an aluminumstay according to a tenth embodiment of the present invention.

FIG. 24A is a cross-sectional view of a bulging jig according to thetenth embodiment of the present invention.

FIG. 24B is a cross-sectional view of a steel bumper beam and analuminum stay having the bulging jig inserted therein, according to thetenth embodiment of the present invention.

FIG. 25A is a cross-sectional view illustrating a state before aclinching process according to the tenth embodiment of the presentinvention.

FIG. 25B is a cross-sectional view illustrating a state after theclinching process according to the tenth embodiment of the presentinvention.

FIG. 26A is a cross-sectional view illustrating a state where thebulging jig has been removed after the clinching process according tothe tenth embodiment of the present invention.

FIG. 26B is a cross-sectional view taken along line XXVI-XXVI in FIG.26A.

FIG. 27A is a perspective view of an aluminum pipe according to aneleventh embodiment of the present invention.

FIG. 27B is a cross-sectional view illustrating a state before aclinching process, taken along line XXVI-XXVI in FIG. 27A.

FIG. 27C is a cross-sectional view illustrating a state after theclinching process, taken along line XXVI-XXVI in FIG. 27A.

FIG. 27D is a plan view of the aluminum pipe and rubber pieces accordingto the eleventh embodiment of the present invention.

FIG. 27E is a plan view of the aluminum pipe and rubber pieces with adifferent shape, according to the eleventh embodiment of the presentinvention.

FIG. 27F is a plan view of the aluminum pipe, rubber pieces, andL-shaped angles according to the eleventh embodiment of the presentinvention.

FIG. 28A is a cross-sectional view illustrating a state before aclinching process according to a twelfth embodiment of the presentinvention.

FIG. 28B is a cross-sectional view illustrating a state after theclinching process according to the twelfth embodiment of the presentinvention.

FIG. 29A is a plan view illustrating a state before and after aclinching process according to a thirteenth embodiment of the presentinvention.

FIG. 29B is a plan view illustrating a state before and after theclinching process according to the thirteenth embodiment of the presentinvention.

FIG. 29C is a front view illustrating a state before the clinchingprocess according to the thirteenth embodiment of the present invention.

FIG. 29D is a front view illustrating a state after the clinchingprocess when a fixation jig according to the thirteenth embodiment ofthe present invention is not used.

FIG. 29E is a front view illustrating a state after the clinchingprocess when the fixation jig according to the thirteenth embodiment ofthe present invention is used.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below withreference to the appended drawings. In the following description, termsthat express directions and positions (such as “upper side” and “lowerside”) are sometimes used, but these terms are used for providing aneasier understanding of the present invention and are not to limit thetechnical scope of the invention. Furthermore, the following descriptionmerely relates to examples of embodiments of the present invention andis not intended to limit the application or the purpose of theinvention.

Although materials of individual components are exemplified in theembodiments described below, the materials of the components in all ofthe embodiments are particularly not limited to the exemplifiedmaterials, and the present invention is applicable to arbitrarymaterials.

First Embodiment

A method for joining a steel component (first member) 10 and an aluminumpipe (second member) 20 together by clinching will be described withreference to FIGS. 1A to 2D.

As shown in FIG. 1A, the steel component 10 is composed of high-tensilesteel and has a shape of a channel. The steel component 10 includes abottom wall (first section) 11, two side walls 12 and 13 extendingvertically upward from the base wall 11, and upper walls 14 extendinghorizontally outward from the two side walls 12 and 13. The bottom wall11 is provided with a hole (first hole) 15 in which the aluminum pipe 20is fittable. The aluminum pipe 20 is composed of an aluminum alloy, hasa hollow and circular cross-sectional shape, and extends along an axisL. The axis L extends through the center of the aluminum pipe 20 andthrough the center of the hole 15 in the steel component 10.

As shown in FIG. 1B, with regard to the aluminum pipe 20 and the steelcomponent 10, the aluminum pipe 20 expands from the inner side towardthe outer side so that an upper edge 21 thereof in the drawing ispressed and bent, whereby the aluminum pipe 20 becomes clinched to thehole 15 in the steel component 10. The hole 15 in the steel component 10preferably has a shape analogous to the cross-sectional shape of thealuminum pipe 20 and a size that is as small as possible within a rangein which the aluminum pipe 20 is fittable therein.

The steel component 10 and the aluminum pipe 20 are clinched together inaccordance with the following procedure.

As shown in FIGS. 2A to 2D, the steel component 10 and the aluminum pipe20 are clinched together by using a rubber piece (elastic body) 30.

First, as shown in FIG. 2A, the aluminum pipe 20 is fitted into the hole15 in the steel component 10, the rubber piece 30 is inserted into thealuminum pipe 20, and the components are set in a pressing device 40.Alternatively, the aluminum pipe 20 may be fitted into the hole 15 in astate where the rubber piece 30 is inserted in the aluminum pipe 20. Thepressing device 40 includes an indenter 43 and a strike plate 42. Theindenter 43 has a flat lower surface and uses the lower surface to pressagainst the steel component 10 or the rubber piece 30. The strike plate42 has a flat upper surface, and the steel component 10 and the rubberpiece 30 are placed on the upper surface. The rubber piece 30 has acolumnar shape with a diameter that allows it to be insertable into thealuminum pipe 20, and has an overall length that is larger than that ofthe aluminum pipe 20. Therefore, when in the set state, the rubber piece30 partially protrudes from the upper end of the aluminum pipe 20. Thus,when the pressing device 40 begins pressing such that the strike plate42 and the indenter 43 relatively approach each other, the rubber piece30 is pressed first. However, the rubber piece 30 does not necessarilyhave to protrude from the upper end of the aluminum pipe 20, and mayalternatively be flush with the upper end of the aluminum pipe 20 or beaccommodated therein.

Next, as shown in FIG. 2B, the pressing device 40 applies a compressiveexternal force to the rubber piece 30 along the axis L. The rubber piece30 dimensionally enlarges in the diameter direction as its sizedecreases along the axis L. Accordingly, the rubber piece 30 is causedto elastically deform (expand) outward from the axis L, thereby causingthe aluminum pipe 20 to expand. Then, as shown in FIG. 2C, the aluminumpipe 20 is further expanded by being further compressed by the pressingdevice 40. At the same time, the upper edge 21 in the drawing is pressedand bent toward the steel component 10, so that the aluminum pipe 20becomes clinched to the steel component 10.

After the clinching process, the rubber piece 30 from which thecompressive force of the pressing device 40 has been removed restoresits original shape with its own elastic force, as shown in FIG. 2D, sothat the rubber piece 30 can be readily removed from the aluminum pipe20.

According to this method, the rubber piece 30 is expanded outward sothat the aluminum pipe 20 expands uniformly, thereby preventing localdeformation and reducing the load on the members 10 and 20. This isbecause the aluminum pipe 20 can be uniformly deformed by utilizing theproperties in which the rubber piece 30 compressed along the axis Lexpands uniformly from the inner side toward the outer side. Therefore,fit accuracy can be improved, thereby achieving increased jointstrength. Moreover, this is an easier method, as compared with anelectromagnetic forming method or other machining methods.

An electromagnetic forming method is usable only on electricallyconductive materials and has limitations with respect to cross-sectionalshapes and dimensions depending on coils to be used. In contrast, thismethod is not dependent on materials and has no limitations related tocross-sectional shapes and dimensions. Moreover, since the method isexecutable in a facility that applies a compressive force to the rubberpiece 30, an electrical facility that requires a large-capacitycapacitor, as in the electromagnetic forming method, is not necessary.

According to this method, two members can be joined together, so that amulti-material process can be readily executed at low cost. Therefore,as described above, this method can be used on members composed ofvarious materials other than the two components composed of high-tensilesteel and an aluminum alloy. The same applies to the subsequentembodiments.

The material used as the rubber piece 30 to be inserted into thealuminum pipe 20 is preferably, for example, urethane rubber,chloroprene rubber, CNR rubber (chloroprene rubber+nitrile rubber), orsilicon rubber. Moreover, it is preferable that the rubber piece 30 havea Shore A hardness of 30 or higher.

A member to be inserted into the aluminum pipe 20 is not limited to therubber piece 30. For example, as shown in FIGS. 3A and 3B, a fluidsealing member 32 having gas or liquid sealed therein may be used inplace of the rubber piece 30. Other members that expand outward inaccordance with a compressive force so as to expand the aluminum pipe 20are also usable. It is preferable that the member deforms uniformly likethe rubber piece 30 when expanding outward in response to a compressiveforce.

Furthermore, as shown in FIGS. 4A and 4B, the shape and size of the hole15 provided in the bottom wall 11 of the steel component 10 do not haveto be analogous to the cross-sectional shape of the aluminum pipe 20 tobe fitted thereto. Specifically, a steel component 10 having a circularhole 15 and an aluminum pipe 20 having a rectangular cross-sectionalshape may be clinched together as in FIG. 4A, or a steel component 10having a rectangular hole 15 and an aluminum pipe 20 having a circularcross-sectional shape may be clinched together as in FIG. 4B.

Furthermore, as shown in FIGS. 5A to 5C, a burring process (flange-upprocess) may be performed on the hole 15 for preventing deformation ofthe steel component 10, for reducing damages to the aluminum pipe 20,and for increasing the clinching strength. Conceivable shapes obtainedas a result of the burring process include, for example, variouscross-sectional shapes shown in FIGS. 5A to 5C. In FIG. 5A, a shouldersection 15 a has a large radius. In FIG. 5B, the shoulder section 15 ais chamfered. In FIG. 5C, a rolling process is employed. Accordingly,even in a case where the steel component 10 has high strength, crackingof the steel component 10 as a result of machining can be effectivelyprevented.

The burring process may be performed in the upward direction or thedownward direction in the drawings. Preferably, as indicated by atwo-dot chain line in FIG. 2A, the burring process is performed in thedownward direction in the drawing such that a part that is bent as aresult of the burring process does not appear on the top surface of thesteel component 10.

As shown in FIGS. 6A and 6B, there are various conceivable shapes, suchas a circular shape (see FIG. 6A) or a rectangular shape (see FIG. 6B),for the hole 15 that is to undergo the burring process. In particular,in a case where the hole 15 is polygonal, corner sections 15 b may becut out, and only straight side sections 15 c may be bent upward, asshown in FIG. 6B, so that the corner sections 15 b can be prevented fromcracking.

Second Embodiment

A joining method according to this embodiment shown in FIGS. 7A and 7Bis similar to that in the first embodiment in FIGS. 2A to 2D except fora feature related to an outer-frame mold 41. Therefore, parts identicalto those in the configuration shown in FIGS. 2A to 2D will be given thesame reference signs, and descriptions thereof will be omitted.

As shown in FIG. 7A, in this embodiment, the steel component 10 and thealuminum pipe 20 are clinched together by using the outer-frame mold 41.The outer-frame mold 41 has a cylindrical shape concentric with thealuminum pipe 20. The outer-frame mold 41 is disposed between the strikeplate 42 and the steel component 10 and at the outer side of thealuminum pipe 20. When set in the pressing device 40, the aluminum pipe20 and the outer-frame mold 41 have a gap therebetween. By applyingpressure using the indenter 43 in this state, the aluminum pipe 20 canconform to the shape of the inner surface of the outer-frame mold 41when the aluminum pipe 20 expands, as shown in FIG. 7B.

According to this method, as shown in FIGS. 8A to 8C, the inner surfaceof the outer-frame mold 41 may have various polygonal shapes, such as ahexagonal shape (see FIG. 8B) or a cross shape (see FIG. 8C), inaddition to the cylindrical shape (see FIG. 8A). With regard to theseshapes, an appropriate shape can be selected in view of, for example,component performance. For example, if the aluminum pipe 20 is a bumperstay, which is one of automobile components, the inner surface of theouter-frame mold 41 may be given small recesses and protrusions so thatthese small recesses and protrusions are transferred onto the aluminumpipe 20, thereby achieving enhanced performance for absorbing impactenergy in the event of a collision.

Third Embodiment

A joining method according to this embodiment shown in FIGS. 9A to 10Bis similar to that in the first embodiment in FIGS. 2A to 2D except fora feature related to an expanding region 22 of the aluminum pipe 20.Therefore, parts identical to those in the configuration shown in FIGS.2A to 2D will be given the same reference signs, and descriptionsthereof will be omitted.

As shown in FIG. 9A, in this embodiment, the rubber piece 30 to beinserted into the aluminum pipe 20 is reduced in length, such that therubber piece 30 is disposed only near the joining section of thealuminum pipe 20. Moreover, the strike plate 42 has a columnarprotrusion 42 a extending upward. The protrusion 42 a is inserted intothe aluminum pipe 20 and supports the rubber piece 30. In other words,the lower end of the rubber piece 30 is in contact with the upper end ofthe protrusion 42 a, and the upper end of the rubber piece 30 is incontact with the lower end of the indenter.

According to this method, an outward expanding force does not act on thepart where the rubber piece 30 is not disposed. Thus, as shown in FIG.9B, the expanding region 22 of the aluminum pipe 20 is limited, so thatthe aluminum pipe 20 and the steel component 10 can be clinched togetherby causing only the region near the joining section of the aluminum pipe20 to expand. Selection of whether the aluminum pipe 20 is to besubstantially entirely deformed as in the first and second embodimentsdescribed above or whether the aluminum pipe 20 is to be partiallydeformed as in this embodiment may be made, as appropriate, based on,for example, the relationship with the component performance.

As shown in FIGS. 10A and 10B, a cylindrical outer-frame mold 44 thatregulates expansion of the aluminum pipe 20 may be disposed therearound.The outer-frame mold 44 has, at the upper end thereof, a large-diametersection 44 a with a large inner diameter near the joining section so asto expand only near the joining section. The inner diameter excludingthat of the large-diameter section 44 a is substantially equal to theouter diameter of the aluminum pipe 20. Therefore, by using theouter-frame mold 44, the expanding region 22 can be controlled with highaccuracy such that the aluminum pipe 20 expands only near the joiningsection.

Fourth Embodiment

A joining method according to this embodiment shown in FIGS. 11A and 11Bis similar to that in the third embodiment in FIGS. 10A and 10B exceptfor a feature related to the shape of the indenter 43. Therefore, partsidentical to those in the configuration shown in FIGS. 10A and 10B willbe given the same reference signs, and descriptions thereof will beomitted.

As shown in FIG. 11A, the indenter 43 included in the pressing device 40according to this embodiment has a downwardly-tapered truncated-coneshape and has a protrusion 43 a and a brim 43 b. Sometimes, a highforming force is required for expanding the edge 21 of the aluminum pipe20 protruding upward from the steel component 10, and there are caseswhere the clinching is insufficient with the deformation of the rubberpiece 30 alone or the durability of the rubber piece 30 may become aproblem due to large deformation thereof. In such cases, the methodaccording to this embodiment is effective.

As shown in FIG. 11B, at the final stage of the forming process, theupper edge 21 of the aluminum pipe 20 protruding upward from the steelcomponent 10 is pressed and expanded outward directly by the protrusion43 a of the indenter 43 without the intervention of the rubber piece 30,and is further bent toward the steel component 10. This enables moresecure clinching. Moreover, the durability of the rubber piece 30 isimproved since excessive load does not act on the rubber piece 30.

Fifth Embodiment

A joining method according to this embodiment shown in FIGS. 12A and 12Bis similar to that in the first embodiment in FIGS. 2A to 2D except fora feature related to the shapes of the indenter 43 and the strike plate42. Therefore, parts identical to those in the configuration shown inFIGS. 2A to 2D will be given the same reference signs, and descriptionsthereof will be omitted.

As shown in FIG. 12A, in this embodiment, the strike plate 42 includes acolumnar protrusion 42 a extending upward and a brim 42 b providedaround the protrusion 42 a. The indenter 43 includes a columnarprotrusion 43 a extending downward and a brim 43 b provided around theprotrusion 43 a. The protrusions 42 a and 43 a are inserted in thealuminum pipe 20.

As shown in FIG. 12B, when performing pressing, the brims 42 b and 43 bcome into contact with the respective ends of the aluminum pipe 20.Thus, the brims 42 b and 43 b apply compressive forces along the axis Lonto the aluminum pipe 20.

According to this method, the aluminum pipe 20 is also compressed alongthe axis L so as to assist with outward expansion of the aluminum pipe20. Specifically, together with the expanding force applied by therubber piece 30 from the inner side of the aluminum pipe 20, thealuminum pipe 20 can be expanded more reliably, thereby enablingclinching.

As shown in FIGS. 13A and 13B, it is also effective to dispose an outerframe 45 at the outer side of a part of the aluminum pipe 20 that is notto be expanded (i.e., the edge 21 in this embodiment). The outer frame45 is cylindrical and is disposed around the edge 21 of the aluminumpipe 20. By disposing the outer frame 45, deformation of the edge 21 ofthe aluminum pipe 20 is regulated, so that a shape according to theintended use can be obtained.

Sixth Embodiment

A joining method according to this embodiment shown in FIGS. 14A to 17Bis similar to that in the first embodiment in FIGS. 2A to 2D except fora feature related to the number of joining sections. Therefore, partsidentical to those in the configuration shown in FIGS. 2A to 2D will begiven the same reference signs, and descriptions thereof will beomitted.

As shown in FIG. 14A, in this embodiment, the steel component 10 and thealuminum pipe 20 are clinched together at two locations. The steelcomponent 10 includes a bottom wall 11, an upper wall (second section)14 disposed parallel to the bottom wall 11, and two side walls 12 and 13connecting these walls, all of which constitute a closed cross section.The bottom wall 11 is provided with a hole 15 (first hole). The upperwall 14 is provided with a hole 17 (second hole). As shown in FIG. 14B,the aluminum pipe 20 is clinched to these two holes 15 and 17.

FIG. 16 is a cross-sectional view during a clinching process. In theclinching process performed on the two holes 15 and 17, the indenter 43is used to press and bend the edge 21 of the aluminum pipe 20 toward thesteel component 10 as in the first embodiment, and the aluminum pipe 20is further expanded so as to be clinched to the upper hole 17 in thedrawing. The aluminum pipe 20 is clinched to the lower hole 15 in thedrawing by being simply expanded.

By performing clinching at two locations as in this embodiment, thejoint strength can be further increased, as compared with the case whereclinching is performed at a single location. In particular, theclinching method using the rubber piece 30 is the same as the case whereclinching is performed at a single location in terms of the facilityused, and is thus effective since the method can easily be used whenperforming clinching at a plurality of locations.

The shape of the steel component 10 or the aluminum pipe 20 whenperforming clinching at two locations is not limited to the above. Forexample, the steel component 10 may have a hat-channel shape, as shownin FIGS. 15A and 15B, or another shape.

Furthermore, as shown in FIG. 17A, the entire aluminum pipe 20 may befreely expanded when performing the clinching process. By using theouter-frame mold 44 described with reference to FIGS. 7A and 7B, onlythe regions of the aluminum pipe 20 near the joining sections may beclinched by being expanded, as shown in FIG. 17B.

Seventh Embodiment

A joining method according to this embodiment shown in FIGS. 18A and 18Bis similar to that in the sixth embodiment in FIG. 16 except forfeatures related to joining locations and bead sections 12 a and 13 a.Therefore, parts identical to those in the configuration shown in FIG.16 will be given the same reference signs, and descriptions thereof willbe omitted.

As shown in FIGS. 18A and 18B, in the steel component 10 according tothis embodiment, the two side walls 12 and 13 are respectively providedwith the bead sections 12 a and 13 a. The bead sections 12 a and 13 aare inward protrusions and extend along the axis L. The aluminum pipe 20is entirely clinched to the hole 15 in the bottom wall 11 and to thebead sections 12 a and 13 a of the two side walls 12 and 13.

As shown in FIG. 18B, the aluminum pipe 20 and the steel component 10are clinched together by including the bead sections 12 a and 13 a ofthe side walls 12 and 13 so that the joint strength can be furtherincreased. Moreover, because the aluminum pipe 20 and the steelcomponent 10 are clinched together by including the bead sections 12 aand 13 a, rotation of the aluminum pipe 20 relative to the steelcomponent 10 can be regulated. Accordingly, the bead sections 12 a and13 a are effective for preventing the aluminum pipe 20 from rotating.Alternatively, for preventing the aluminum pipe 20 from rotating, it isalso effective to give the edge of the hole 15 a cutout shape or a shapeother than the circular shape.

Eighth Embodiment

A joining method according to this embodiment shown in FIG. 19 issimilar to that in the seventh embodiment in FIG. 18A except for afeature related to split rubber pieces 30. Therefore, parts identical tothose in the configuration shown in FIG. 18A will be given the samereference signs, and descriptions thereof will be omitted.

As shown in FIG. 19, in this embodiment, the rubber piece 30 is splitnear the hole 15. According to this method, the rubber piece 30 is splitat the hole 15, that is, at the joining section, so that deformation ofthe hole 15 and the bottom wall 11 of the steel component 10 can beprevented. Specifically, because the rubber piece 30 is split, anexpanding force is not applied to the hole 15, so that the hole 15 andthe bottom wall 11 can maintain their original shapes.

Furthermore, as shown in FIGS. 20A and 20B, it is preferable that atabular plate 31 be inserted between the rubber pieces 30 split at thejoining section and inserted in the aluminum pipe 20. The plate 31 maybe composed of metal or resin so long as it is strong enough not todeform in response to a compressive force received from the rubber piece30, and preferably has a thickness of 15 mm or smaller.

According to this method, the plate 31 exists in the joining section sothat deformation of the hole 15 and the bottom wall 11 of the steelcomponent 10 can be prevented more reliably. Because the plate 31 doesnot expand, an expanding force is not applied to the hole 15, so thatthe hole 15 and the bottom wall 11 can maintain their original shapes.

As an alternative to FIG. 20A in which the rubber piece 30 is split andthe plate 31 is disposed between the split pieces, a rubber piece 30partially composed of a different material may be used, as in FIG. 20B.In FIG. 20B, the rubber piece is a non-split single piece but has ahigh-hardness section 30 a near the joining section. Specifically, therubber piece 30 has a high hardness only in a part thereof near thejoining section. Thus, this high-hardness section 30 a has a functionsimilar to that of the plate 31, so that the hole 15 and the bottom wall11 can maintain their original shapes.

Ninth Embodiment

A joining method according to this embodiment shown in FIGS. 21A to 22Bis similar to that in the fifth embodiment in FIGS. 9A and 9B exceptthat the steel component 10 is replaced with a cylindrical resinous tubecomponent 50. Therefore, parts identical to those in the configurationshown in FIGS. 9A and 9B will be given the same reference signs, anddescriptions thereof will be omitted.

As shown in FIGS. 21A and 21B, in this embodiment, the cylindricalresinous tube component 50 having a flange at the upper end thereof andthe aluminum pipe 20 are clinched together. Like the resinous tubecomponent 50, the target member does not have to be tabular or becomposed of metal. As mentioned above, the aluminum pipe 20 deformsoutward in response to a compressive force applied along the axis L fromthe rubber piece 30 so as to expand. Therefore, this method is notlimited to be used on electrically conductive materials, as in theelectromagnetic forming method, and can also be used on resin materials,and the shape is not limited to the tabular shape.

FIGS. 22A and 22B are cross-sectional views illustrating states beforeand after the resinous tube component and the aluminum pipe in FIG. 21Aare clinched together. As shown in FIGS. 22A and 22B, the aluminum pipe20 is clinched to the cylindrical resinous tube component 50 by beingexpanded at the opposite ends thereof.

Tenth Embodiment

An example in which the present invention is applied to a bumper, whichis one of automobile components, will now be described.

As shown in FIG. 23, a cylindrical aluminum stay (second member) 120 isclinched to a closed-cross-section steel bumper beam (first member) 110having a partition 111 in the middle. The steel bumper beam 110 hasopenings 113 and 113 at opposite sides thereof. The openings 113 and 113are separated from each other by the partition 111. For illustrativepurposes, a top plate 114 (see FIG. 26A) of the steel bumper beam 110 isshown in a removed state in FIG. 23. As shown in FIG. 24A, for theimplementation, a bulging jig 150 including a round-rod-shaped rubberpiece 130, a tabular steel plate 131, and a narrow round rod 140composed of steel is used. A through-hole 112 into which the narrowround rod 140 is insertable is provided in the middle of the rubberpiece (elastic body) 130 and the tabular plate 131. One end of the roundrod 140 is provided with a brim 141 for preventing the rubber piece 130from falling out. The rubber piece 130 is split into two, one of whichis provided with a countersunk hole 132 to which the brim 141 of theround rod 140 is fittable. The tabular plate 131 is placed on the rubberpiece 130 with the countersunk hole 132 facing downward, the otherrubber piece 130 is placed thereon, and the round rod 140 issubsequently inserted from below. The plate 131 has a circular shapewith an outer diameter of ϕ83.5 mm and a thickness of 10 mm. The rubberpieces 130 used are composed of urethane rubber and have a circularshape with an outer diameter of ϕ83.5 mm, a length of 50 mm, and a ShoreA hardness of 90.

FIG. 24B illustrates a state where the aluminum stay 120 is fitted inthe hole (hole) 112 (see FIG. 23) provided in the steel bumper beam 110,and the aforementioned bulging jig 150 is inserted in the aluminum stay120. As shown in FIG. 23, the steel bumper beam 110 is processed into aclosed-cross-sectional shape having a partition 111 in the middle byroll-forming a 1470-MPa-class cold-rolled steel plate having a thicknessof 1.4 mm and has a circular hole 112 having an outer diameter of ϕ90.2mm formed in the joining section with the aluminum stay 120. In thiscase, the partition 111 in the middle is partially removed. The aluminumstay 120 is formed of a circular pipe composed of an aluminum alloyA6063 and having a thickness of 3 mm, an outer diameter of ϕ90 mm, and alength of 150 mm.

Next, a clinching process shown in FIGS. 25A and 25B will be described.FIG. 25A illustrates a state where the steel bumper beam 110, thealuminum stay 120, and the bulging jig 150 are set on a lower mold 152,and a presser jig 151 is disposed thereon. This state is set in thepressing device 40 (see FIGS. 2A to 2D), and a slide having the presserjig 151 set thereon is lowered so as to apply a compressive force to therubber pieces 130. In this case, pressure along the axis L of thealuminum pipe 20 is not applied, as shown in FIGS. 9A and 9B.

FIG. 25B illustrates a state where the slide is at the bottom deadcenter. The rubber pieces 130 are compressed by the presser jig 151 soas to expand in the horizontal direction, thereby bulge-forming thealuminum stay 120. Because the tabular plate 131 is inserted, the jointsurface of the steel bumper beam 110 does not receive an excessive forceso that undesired deformation is suppressed, whereby a clinching processwith high fit accuracy is completed.

FIGS. 26A and 26B illustrate the steel bumper beam 110 and the aluminumstay 120 upon completion of the clinching process. FIG. 26A is across-sectional view of the steel bumper beam 110 and the aluminum stay120 in a clinched state, and FIG. 26B is a cross-sectional view takenalong line XXVI-XXVI. This embodiment is characterized in that the jointstrength is high since clinching can be achieved at the middle partition111 in addition to clinching at the hole 112 provided in the steelbumper beam 110 due to expansion of the aluminum stay 120 caused by therubber pieces 130 shown in FIG. 26B.

Eleventh Embodiment

A joining method according to this embodiment shown in FIGS. 27A to 27Fis similar to that in the fifth embodiment in FIGS. 9A and 9B exceptthat the aluminum pipe 20 has a partition wall 23 therein and aplurality of rubber pieces 30 are inserted in the aluminum pipe 20.Therefore, parts identical to those in the configuration shown in FIGS.9A and 9B will be given the same reference signs, and descriptionsthereof will be omitted.

As shown in FIG. 27A, the aluminum pipe 20 according to this embodimenthas outer walls 24 extending along the axis L and having a rectangularshape in cross section and the partition wall 23 provided inside theouter walls 24. The space inside the aluminum pipe 20 is divided intofour spaces by the partition wall 23 having a cross shape in plan view.By providing the partition wall 23 in this manner, the strength of thealuminum pipe 20 can be increased. The cross-sectional shape is notlimited to the rectangular shape and may be a freely-chosen shape.

As shown in FIGS. 27B and 27C, the indenter 43 according to thisembodiment is provided with a cutout 43 c in conformity to the shape ofthe partition wall 23. By providing the cutout 43 c, the clinchingprocess can be completed without interference with the aluminum pipe 20even when the rubber pieces 30 are pressed.

Accordingly, because the clinching process is performed by using theplurality of rubber pieces 30 (i.e., four in this embodiment),concentration of stress caused by deformation can be prevented, so thatthe load on the steel component 10 and the aluminum pipe 20 can bereduced.

The shape of each rubber piece 30 according to this embodiment is notlimited in particular. For example, as shown in FIG. 27D, the corners ofthe four inserted rubber pieces 30 may be round-chamfered so as toreduce the load on the corners of the aluminum pipe 20, therebypreventing cracking and damaging. As shown in FIG. 27E, C-chamfering maybe performed, similarly to round-chamfering. As shown in FIG. 27F,although the shape of the four inserted rubber pieces 30 is columnar,steel L-shaped angles 46 may be disposed along the partition wall 23within the aluminum pipe 20. Consequently, the load on the partitionwall 23 can be reduced, thereby suppressing deformation.

Twelfth Embodiment

A joining method according to this embodiment shown in FIGS. 28A and 28Bis similar to that in the fifth embodiment in FIGS. 9A and 9B exceptthat the steel component 10 and the aluminum pipe 20 are joined togetherin an inclined state. Therefore, parts identical to those in theconfiguration shown in FIGS. 9A and 9B will be given the same referencesigns, and descriptions thereof will be omitted.

As shown in FIGS. 28A and 28B, the aluminum pipe 20 according to thisembodiment has an end surface 25 inclined relative to the axis L. Thesteel component 10 is bent and is placed on an inclined surface 42 c.The aluminum pipe 20 is placed on the inclined surface 42 c in a statewhere the inclined end surface 25 is in contact therewith, and isclinched to the steel component 10. Therefore, the steel component 10and the aluminum pipe 20 are clinched together in an inclined state.Opposite end surfaces 30 b and 30 c of the rubber piece 30 according tothis embodiment are formed and disposed parallel to the inclined endsurface 25 of the aluminum pipe 20. A pressing surface 43 d of theindenter 43 is also formed parallel to the end surfaces 30 b and 30 c ofthe rubber piece 30.

Accordingly, this method can be used for clinching the steel component10 and the aluminum pipe 20 together in an inclined state, which isoften seen from a practical standpoint. Specifically, the opposite endsurfaces 30 b and 30 c of the rubber piece 30 are given the same angleas the joining angle, so that the rubber piece 30 expands uniformly,whereby the aluminum pipe 20 can be expanded uniformly.

Thirteenth Embodiment

A joining method according to this embodiment shown in FIGS. 29A to 29Dis similar to that in the fifth embodiment in FIGS. 9A and 9B exceptthat the steel component 10 is joined in a state where deformationthereof is restrained by a fixation jig 47. Therefore, parts identicalto those in the configuration shown in FIGS. 9A and 9B will be given thesame reference signs, and descriptions thereof will be omitted.

As shown in FIGS. 29A and 29B, the steel component 10 according to thisembodiment has a bottom wall 11 and an upright wall 18 extending alongthe axis L from the bottom wall 11. The cross-sectional shape of thealuminum pipe 20 before the clinching process is not particularlylimited and may be circular (see the dashed line in FIG. 29A) orrectangular (see the dashed line in FIG. 29B). The fixation jig 47 forsuppressing deformation is provided at the outer side of the steelcomponent 10. The fixation jig 47 is disposed along the upright wall 18and is fixed from the directions of the arrows in the drawings so as notto move outward. Although the fixation jig 47 used in this embodiment istabular, the shape of the fixation jig 47 is not limited to this shapeand may alternatively be a freely-chosen shape that can suppressdeformation.

As shown in FIGS. 29C to 29E, in a case where the fixation jig 47 is notprovided, the steel component 10 may deform in a warping manner whenclinching is performed (see FIG. 29D). However, with the fixation jig47, deformation of the steel component 10 is restrained, so thatdeformation, such as warping, of the steel component 10 caused byexpansion of the aluminum pipe 20 can be suppressed (see FIG. 29E).

REFERENCE SIGNS LIST

-   -   10 steel component (first member)    -   11 bottom wall (first section)    -   12, 13 side wall    -   12 a, 13 a bead section    -   14 upper wall (second section)    -   15 hole (first hole)    -   15 a shoulder section    -   15 b corner section    -   15 c straight side section    -   17 hole (second hole)    -   18 upright wall    -   20 aluminum pipe (second member)    -   21 edge    -   22 expanding region    -   23 partition wall    -   24 outer wall    -   25 end surface    -   30 rubber piece (elastic body)    -   30 a high-hardness section    -   30 b, 30 c end surface    -   31 plate    -   32 fluid sealing member    -   40 pressing device    -   41 outer-frame mold    -   42 strike plate    -   42 a protrusion    -   42 b brim    -   42 c inclined surface    -   43 indenter    -   43 a protrusion    -   43 b brim    -   43 c cutout    -   43 d pressing surface    -   44 outer-frame mold    -   44 a large-diameter section    -   45 outer frame    -   46 L-shaped angle    -   47 fixation jig    -   50 resinous tube component    -   110 steel bumper beam (first member)    -   111 partition    -   112 hole (hole)    -   113 opening    -   114 top plate    -   120 aluminum stay (second member)    -   130 rubber piece (elastic body)    -   131 plate    -   132 countersunk hole    -   140 round rod    -   141 brim    -   150 bulging jig    -   151 presser jig    -   152 lower mold

1. A method for joining members, comprising: preparing a first memberand a hollow second member, the first member having a first sectionprovided with a first hole; fitting the second member into the firsthole in the first member so as to cause the second member to extendthrough the first section; inserting an elastic body into the secondmember; compressing the elastic body in a direction of an axis of thesecond member so as to cause the elastic body to expand from an innerside toward an outer side, and thus causing at least a part of thesecond member fitted in the first hole to expand so as to becomeclinched to the first section; and wherein the first member has a convexbead part, which arounds the first hole and extends in axial directionof the surface of the first member; and the convex bead part is fittedto second member to be expanded together with second member.
 2. Themethod for joining members according to claim 1, wherein a shape of thefirst hole in the first member is analogous to a cross-sectional shapeof the part of the second member fitted in the first hole.
 3. The methodfor joining members according to claim 1, wherein an outer-frame mold isdisposed at the outer side of the second member, and at least a part ofthe second member is formed to extend along the outer-frame mold so asto become clinched.
 4. The method for joining members according to claim1, wherein an outer-frame mold is disposed at the outer side of thesecond member, and clinching is performed while partially limitingexpansion of the second member by using the outer-frame mold.
 5. Themethod for joining members according to claim 1, wherein the secondmember is also compressed in the direction of the axis when the elasticbody is compressed.
 6. The method for joining members according to claim1, wherein an edge of the first hole is burred.
 7. The method forjoining members according to claim 1, wherein a surface different from asurface provided with the first hole has a bead section protruding inthe direction of the axis, and clinching is performed by including thebead section.
 8. The method for joining members according to claim 1,wherein the first member includes a second section having a second holeand is clinched to the second member at the first hole and the secondhole.
 9. The method for joining members according to claim 1, whereinthe elastic body is split at a joining section between the first memberand the second member.
 10. The method for joining members according toclaim 1, wherein a plate is inserted between split pieces of the elasticbody.
 11. The method for joining members according to claim 1, whereinthe second member includes an outer wall provided with a partition walltherein and extending in the direction of the axis, and whereinclinching is performed by inserting a plurality of the elastic bodies inspaces partitioned by the partition wall.
 12. The method for joiningmembers according to claim 1, wherein the second member includes an endsurface inclined relative to the axis, and wherein opposite end surfacesof the elastic body in the direction of the axis are parallel to theinclined surface.
 13. The method for joining members according to claim1, wherein the first member includes an upright wall parallel to theaxis, and wherein clinching is performed while restraining deformationof the upright wall by using a fixation jig.